1. Field of the Invention
The present invention relates to a method of performing color interpolation of image data.
2. Description of the Background Art
A CCD image pickup device used in a digital camera or the like performs photoelectric conversion of light received through a color filter and outputs image data. As this color filter, an RGB color filter, a YMCK color filter or the like is used. Through a 1-chip color CCD, image data of one color is outputted for one pixel. For example, through an RGB color filter, image data of R (Red) component, G (Green) component or B (Blue) component is outputted for one pixel.
With respect to image data outputted from a 1-chip color CCD, since only image data of one single color is outputted for each pixel, interpolation is performed on image data of the other color components. For this interpolation, various algorithms are used.
The interpolation, however, is an operation of estimating image data of a specified pixel from image data of pixels around the specified pixel, and therefore a wrong interpolation is sometimes performed depending on the content of an image. Then, techniques to improve the accuracy of interpolation are disclosed in the following Laid Open Gazettes.
Japanese Patent Application Laid Open Gazette No. 2002-300590 discloses a technique where correlations in vertical and horizontal directions are obtained by calculating the difference of G signals in the vertical direction and that of G signals in the horizontal direction and pixel interpolation and generation of a color difference signal are performed in accordance with the correlations. Japanese Patent Application Laid Open Gazette No. 11-205808 discloses a technique where the correlations in the vertical and horizontal directions are obtained by using G signals and pixel interpolation is performed in accordance with the correlations.
Since the correlations are obtained only by using the G signals in the methods disclosed in the above Laid Open Gazettes, however, these methods have a problem in accuracy of interpolation. Since the correlation in the horizontal or vertical direction is conventionally judged from adjacent pixels (in a narrow area), this causes errors in judgment of correlation in a high frequency range such as an edge portion or a fine line (especially, an area near Nyquist frequency or an area of fine line across pixels). For this reason, there is a problem that the accuracy of interpolation is low when the tendency of pixel drift in either the horizontal or vertical direction is strong.